Electrocorticography (ECoG)

Or intracranial EEG (iEEG), is the practice of using electrodes placed directly on the exposed surface of the brain to record electrical activity from the cerebral cortex. ECoG may be performed either in the operating room during surgery (intraoperative ECoG) or outside of surgery (extraoperative ECoG). Because a craniotomy is required to implant the electrode grid, ECoG is an invasive procedure.

The signals recorded by ECOG and Stereoelectroencephalography (SEEG) have very similar spectral power and phase-amplitude coupling, suggesting that both modalities are comparable from an electrodiagnostic standpoint in delineation of the epileptogenic network 1).

see Cortical stimulation.

The detectability of high frequency oscillations (HFO, >200Hz) in the intraoperative ECoG is restricted by their low signal-to-noise ratio (SNR).

Low-noise amplification improves the detection of the evoked high frequency oscillations (HFO, >200Hz) in recordings with subdural electrodes with low impedance 2).

80 patients underwent intracranial EEG recording for epilepsy surgery planning. Ghosn et al. developed a first-order pharmacokinetic model of the anti-seizure medications (ASMs) administered in the Epilepsy Monitoring Unit (EMU) to generate a continuous metric of the overall ASM load. They then related modeled ASM load to seizure likelihood and severity. They determined the association between the rate of ASM load reduction, the length of hospital stay, and the probability of having a severe seizure. Finally, they used modeled ASM load to predict oncoming seizures.

Seizures occurred in the bottom 50th -percentile of sampled ASM loads across the cohort (p < 0.0001, Wilcoxon sign-rank test), and seizures requiring rescue therapy occurred at lower ASM loads than seizures that did not require rescue therapy (logistic regression mixed effects model, odds ratio = 0.27, p = 0.01). Greater ASM decreases early in the EMU were not associated with an increased likelihood of having a severe seizure, nor with a shorter length of stay.

A pharmacokinetic model can accurately estimate ASM levels for patients in the EMU. Lower modeled ASM levels are associated with increased seizure likelihood and seizure severity. They showed that ASM load, rather than ASM taper speed, is associated with severe seizures. ASM modeling has the potential to help optimize taper strategy to minimize severe seizures while maximizing diagnostic yield 3).

Young JJ, Friedman JS, Panov F, Camara D, Yoo JY, Fields MC, Marcuse LV, Jette N, Ghatan S. Quantitative Signal Characteristics of Electrocorticography and Stereoelectroencephalography: The Effect of Contact Depth. J Clin Neurophysiol. 2019 Mar 26. doi: 10.1097/WNP.0000000000000577. [Epub ahead of print] PubMed PMID: 30925509.
Fedele T, Sch├Ânenberger C, Curio G, Serra C, Krayenb├╝hl N, Sarnthein J. Intraoperative subdural low-noise EEG recording of the high frequency oscillation in the somatosensory evoked potential. Clin Neurophysiol. 2017 Jul 27;128(10):1851-1857. doi: 10.1016/j.clinph.2017.07.400. [Epub ahead of print] PubMed PMID: 28826015.
Ghosn NJ, Xie K, Pattnaik AR, Gugger JJ, Ellis CA, Sweeney E, Fox E, Bernabei JM, Johnson J, Boccanfuso J, Litt B, Conrad EC. A pharmacokinetic model of anti-seizure medication load to guide care in the Epilepsy Monitoring Unit. Epilepsia. 2023 Feb 23. doi: 10.1111/epi.17558. Epub ahead of print. PMID: 36815252.
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